import java.util.Arrays;

public class PriorityQueue {
    public int[] elem;
    public int usedSize;

    public PriorityQueue() {
        elem = new int[10];
    }

    /**
     * 建堆的时间复杂度：
     *
     * @param array
     */
    public void createHeap(int[] array) {
        for (int i = 0; i < array.length; i++) {
            elem[i] = array[i];
            usedSize++;
        }
        for (int i = (usedSize-1-1)/2; i >= 0; i--) {
            shiftDown(i,usedSize);
        }
    }

    /**
     *
     * @param root 是每棵子树的根节点的下标
     * @param len  是每棵子树调整结束的结束条件
     * 向下调整的时间复杂度：O(logn)
     */
    private void shiftDown(int root,int len) {
        int parent = root;
        int child = parent * 2 + 1;
        while (child < len) {
            if (child + 1 < len && elem[child] < elem[child + 1]) {
                child++;
            }
            if (elem[parent] < elem[child]) {
                int tmp = elem[child];
                elem[child] = elem[parent];
                elem[parent] = tmp;
                parent = child;
                child = parent * 2 + 1;
            } else {
                break;
            }
        }
    }


    /**
     * 入队：仍然要保持是大根堆
     * @param val
     */
    public void push(int val) {
        if(isFull()) {
            elem=Arrays.copyOf(elem,elem.length*2);
        }
        elem[usedSize++] = val;

        shiftUp(usedSize-1);
    }

    private void shiftUp(int child) {
        while(child > 0) {
            int parent = (child-1)/2;
            if(elem[child] > elem[parent]) {
                int tmp = elem[child];
                elem[child] = elem[parent];
                elem[parent] = tmp;
            }else{
                break;
            }
            child = parent;
        }
    }

    public boolean isFull() {
        return usedSize == elem.length;
    }

    /**
     * 出队【删除】：每次删除的都是优先级高的元素
     * 仍然要保持是大根堆
     */
    public void pollHeap() {
        if(isEmpty()) {
            return;
        }
        int tmp = elem[0];
        elem[0] = elem[usedSize-1];
        elem[usedSize-1] = tmp;
        usedSize--;
        shiftDown(0,usedSize-1);
    }

    public boolean isEmpty() {
        return usedSize==0;
    }

    /**
     * 获取堆顶元素
     * @return
     */
    public int peekHeap() {
        if(isEmpty()) {
            return -1;
        }
        return elem[0];
    }
}
